Two Australian lawyers say Opposition Leader Belden Namah's challenge has a good chance of success.

Mr Namah launched proceedings on Friday in the National Court of Papua New Guinea, claiming the processing centre was the result of ''many abuses of PNG law and of ministerial powers''.

''Our claim, that the asylum seekers detention scheme is unconstitutional and that the detainees on Manus are held illegally in PNG, has never been legitimately addressed by the government and must now be answered in our highest courts,'' he said.

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The opposition's legal team would also seek an injunction to have asylum seekers released from the processing centre, and to prevent PNG from receiving or detaining any more asylum seekers from Australia.

The memorandum of understanding between Australia and Papua New Guinea - which sets out their agreement on regional processing - breached the asylum seekers' constitutional right to personal liberty, Mr Namah said.

Julian Burnside, QC, who ran an unsuccessful challenge against the Howard government's Pacific Solution, told Fairfax Media the case appeared to be solid.

''The real strength of the case is in the PNG constitution, because that constitution has a guarantee of liberty,'' he said.

An Australian lawyer working in PNG said the challenge was likely to succeed, because the PNG constitution had a strong bill of rights.

The lawyer, who did not want to be named, said the right to ''liberty of the person'' applied to all people, not just citizens of PNG.

Mr Namah said his challenge asked the courts to declare that the memorandum of understanding was unlawful because it allowed Australia to force asylum seekers to enter PNG territory and allowed the PNG government to deprive them of their liberty as soon as they entered.

A spokesman for Immigration Minister Chris Bowen would not comment on the challenge's prospects and said it was unclear whether Australia would be required to have a role in the court case.

''We are not going to comment on politics or court matters in another country,'' he said.

The spokesman said the memorandum of understanding was binding and working well.